The invention relates to an exhaust gas turbocharger for an internal combustion engine having a turbine wheel and a compressor wheel mounted on a common shaft, wherein the compressor wheel is disposed in a housing having an inlet with an adjustable inlet structure for controlling the air flow to the compressor wheel.
Such an exhaust gas turbocharger is described in DE 100 49 198 A1. This exhaust gas turbocharger comprises a compressor in the intake tract of an internal combustion engine, which compressor is driven via a shaft by a turbine disposed in the exhaust tract. In the turbine, the energy of the exhaust gas is converted into a rotary movement of the turbine wheel. The turbine wheel of the turbine is rotationally fixedly connected by means of a shaft to a compressor wheel of the compressor. The rotary movement of the turbine wheel is transmitted via the shaft to the compressor wheel. By rotation of the compressor wheel, the compressor sucks in intake air and compresses it to a higher charge pressure, under which the intake air is supplied to the cylinders of the internal combustion engine.
In order to avoid, or keep as low as possible, a speed drop of the exhaust gas turbocharger, particularly at low loads and speeds of the internal combustion engine, the compressor of the internal combustion engine can also be operated in the so-called cold-air turbine mode in which a pressure gradient across the compressor is utilized for additionally driving the compressor wheel. In order to improve efficiency, an additional duct is provided in the compressor housing, which additional duct extends approximately parallel to the compressor inlet duct and opens out radially into the compressor inlet duct at the level of the compressor wheel blades. Said additional duct is opened at low loads and speeds, so that the intake air impinges radially on the compressor wheel blades and imparts an additional driving impulse thereto.
It is the object of the present invention to provide an exhaust gas turbocharger whose speed can be kept at a minimum level even during a low load and/or speed mode of operation of the internal combustion engine, in particular in the cold-air turbine mode.